Despite the last few days working - and fine earlier in the day - encountered problem again with Passive mode disabled. Transferring two files, the first was okay and the problem happened about a quarter of the way for the second. Countless reconnecting and trying again no joy, and had to use Core FTP LE.
It appears that at certain times something is happening that causes a problem for WinSCP but cannot see what it is.
For reference, the final part of the log to show differences for not using Passive mode:
> 2017-05-04 14:15:29.697 TYPE A
< 2017-05-04 14:15:29.712 200 Switching to ASCII mode.
> 2017-05-04 14:15:29.713 PORT 10,0,208,136,248,13
< 2017-05-04 14:15:29.728 200 PORT command successful. Consider using PASV.
> 2017-05-04 14:15:29.729 STOR xxxxxxxxxx.txt
. 2017-05-04 14:15:44.506 Timeout detected. (data connection)
. 2017-05-04 14:15:44.507 Copying files to remote side failed.
. 2017-05-04 14:15:44.508 Connection was lost, asking what to do.
. 2017-05-04 14:15:44.508 Asking user:
. 2017-05-04 14:15:44.508 Lost connection. ("Timeout detected. (data connection)","Copying files to remote side failed.")
* 2017-05-04 14:15:45.510 (ESshFatal) **Lost connection.**
* 2017-05-04 14:15:45.510 Timeout detected. (data connection)
* 2017-05-04 14:15:45.510 Copying files to remote side failed.